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A Unified Graphical Representation and Tool for Design and Integration of Components in Heterogeneous Distributed Real-Time Systems

Hugo Andrade, John Breyer, Gerardo Garcia, Jacob Kornerup

National Instruments CorporationAustin, TX, USA

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National Instruments

Distributors

Direct Sales Offices

7 Years• 30 Year Leaders in Computer-Based

Measurement and Automation• 3800 Employees, 1,500 Engineers• Corporate Headquarters in Austin,

Texas– Direct Operations in 40 Countries

• Over 600 Alliance Partners

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Virtual Instrumentation Vision

“To do for test and measurement what the spreadsheet did for financial analysis.”

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Use Case: Distributed Fly-by-Wire HIL Simulation• Challenge

– Integrate 10 distributed nodes executing device models

– Share simulation data and I/O with low latency

• Solution– Implement simulation models on

real-time platforms – Deterministic network used to

share data

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Use Case: Engine HIL Simulation• Challenge: Simulate a 12 cylinder hybrid engine to

test control strategies• Solution: Implement simulation model on real-time

platform

Engine Control Unit (ECU)

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• Structured data flow programming• Compiled graphical development • Target desktop, mobile, industrial,

and embedded• Thousands of out-of-the box

mathematics and signal processing routines

• Seamless connectivity to millions of I/O devices

LabVIEW Graphical Development Environment

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LabVIEW Platforms

Portable

FPGA

Embedded Controllers

PC

Handheld

Industrial Controllers (PXI)

Sensor

Vision System

LabVIEW

DSP/MPU

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State Diagram

Real-Time FPGADistributed

Textual Math Simulation Configuration

C Code Generation

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LabVIEW Shared Variable• Exchanging values when data flow is not appropriate

– Loop to Loop– In a distributed setting– Utilize non-blocking buffers

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Timed Loop in LabVIEW: Specifying a Task

External Timing Source

(What makes me tick)

Configuration(What can I do for you)

Run Time Status(How am I doing)

Run Time Configuration(How can I serve you better)

Final Status(How did I do)

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National Instruments’ Time-Triggered Network• Deterministic communication

– 100 µs to 100 ms network loop rates– ±5 µs clock synchronization between nodes

• Off-the-shelf hardware– Uses second Ethernet interface

• Communication across private network– Traffic is scheduled

• Similar to other time-triggered offerings– FlexRay, TTP, TTCAN, Ethernet PowerLink,

…

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Using Deterministic Ethernet

• User specifies a network cycle time– All traffic is repeated at this interval

• Time-triggered variables– Used on the diagram just like other variables in LabVIEW

• Owning system is the only writer

– Values are communicated during designated time slots within the network cycle

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Using Deterministic Ethernet • Network timing sources

– Fires the Timed Loop when the network event happens– Timing source types

• Network synchronized microsecond• Shared memory block has been reflected• Slot based variable timing sources

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Other uses of shared variable

• Publish and subscribe• Non-blocking FIFOs• Streaming• DMA transfers• IO abstraction• Can you change the model of computation just by changing

variable types?– Without redrawing the diagram

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Time-Triggered Distributed Simulation Use Case

• Separate models for different system components

• Models execute in real-time with synchronized timing

• Capability to switch to real-world I/O

Ethernet

Engine Model

EthernetReal-Time

I/O

RPM, Throttle

Timing, Fueling

Private Ethernet Network

ECU

RPM, Throttle

Timing, Fueling

Ethernet

Engine Model

Ethernet

ECU Model

RPM, Throttle

Timing, Fueling

Private Ethernet Network

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• Create Time-Triggered Shared Variables

• Reserve time slots for variables in network configuration utility

Time-Triggered Distributed Simulation Example

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Time-Triggered Distributed Simulation Example

RealECU

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Capturing the Real-time Behavior

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Separation of Concerns

• Programming abstractions– Diagram describes (abstract) functionality– Variable describes communication style– Timing sources describes events

• System architecture– Platform/ hw architecture

• Real-time, FPGA, Embedded, Desktop– Data transfer– Time, event, data triggering– HW/SW boundary

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Temporal Isolation

• Static schedule of communication• Rigid temporal contract between programs and network

– Between components– Network enforces the global schedule

• If a program runs over, its values will not get communicated in this cycle

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Questions